In a process of manufacturing a semiconductor device, a thin film forming process is performed to form a thin film such as a poly-silicon film, a silicon nitride film and the like on an object to be processed, e.g., a semiconductor wafer, through a process such as chemical vapor deposition (CVD) or the like. In such a thin film forming process, the semiconductor wafer is accommodated into a reaction tube, which is heated at a predetermined temperature, and a film forming gas is supplied into the reaction tube to cause a thermal reaction to the film forming gas. A reaction product generated from the thermal reaction is deposited on a surface of the semiconductor wafer, thus forming a thin film on the surface of the semiconductor wafer.
However, the reaction product generated from the thin film forming process may be deposited (attached) on an interior of a heat treatment apparatus such as an inner wall of the reaction tube, various jigs and the like, as well as on the surface of the semiconductor wafer. When the thin film forming process continues in a state in which the reaction product (extraneous particles) is attached to the interior of the heat treatment apparatus, a stress is generated due to a difference in coefficient of thermal expansion between the extraneous particles and the quartz, which constitutes the reaction tube, and the quartz and the extraneous particles may be peeled by the stress. Consequently, particles are generated by the peeled quartz or extraneous particles and thus the yield of the semiconductor device to be manufactured may be decreased.
In order to solve this problem, a method of cleaning the heat treatment apparatus is suggested. In the method, a cleaning gas, for example, a mixture gas of fluorine and a halogen-containing acidic gas is supplied into the reaction tube, which is heated at a predetermined temperature by a heater, to remove (dry-etch) the reaction product attached to the interior of the heat treatment apparatus.
However, in the method of cleaning the heat treatment apparatus, there is a problem in that the cleaning may be excessively performed or may not be sufficiently performed because the cleaning is performed based on only one of the two conditions including a thickness of an accumulative thin film to be formed and the number of times of performing a thin film forming process, and also because only one type of cleaning recipe is available to perform. Further, there is also a problem in that the cleaning is oftentimes unnecessarily performed.